(K_Gal: This primarily addresses RHPC's issue, but does include some comments regarding yours)
B
RHPC:
Yours is a different issue than that described in the initial post in this thread.
Pages has several auto-correction features, all set in the auto-correction pane of Pages Preferences. The two indicated by the arrows are the significant ones in this thread as started and in your hijack of this thread.

Fix capitalization (blue arrow) applies a format (CAPITAL or UPPER) to the initial letters of 'sentences' and words identified as 'proper nouns' (such as "March") in the spelling dictionary. It performs no action on 'words' that have been typed with initial capitals.

In the examples above, the first two lines were typed with 'Fix capitalization' unchecked. The second pair of lines were typed using exactly the same keystrokes as the first, but with 'Fix capitalization' checked. Note that both occurrences of 'will' are the same in each set.
"Automatically use spell checker suggestions" (red arrow) does precisely what it says: If a 'word' is not found in the spelling dictionary, the spell checker will make a 'best guess' and suggest that as a possible replacement. If the 'Automatically use…" box is checked, then Pages will immediately accept the first suggestion, replacing the 'questionable word' with the spell checkers first ('best') suggestion.
There are at least two solutions to this issue:
Uncheck the box and don't use auto-correction. (works for either of these issues)
Teach the spellchecker the correct spelling of the Polish name. (does not work in the case of march/March, which is part of the base dictionary)
To do this:
- Go Pages (menu) > Preferences... Auto-Correction
- Uncheck the "Automatically use…" box.
- Close Preferences
- Open a new Pages word processing document.
- Type the Polish name.
- Ensure that the spelling and capitalization is correct.
- Right click on the name and choose Learn Spelling.
- Go Pages > Preferences… Auto-Correction
- Recheck the "Automatically use…" box
- Close Preferences.
Done.
Pages (and other applications using the system's spell checker dictionary) will now recognize the spelling of this name and will not 'correct' it.
(K_Gal: Unfortunately, when I tried this on "march" the contextual menu did not include the Learn Spelling option 😟 , probably because the dictionary already 'knew' how to spell "March". I'd suggest using the Provide Pages Feedback item in the Pages message to report this to apple, and request a feature enhancement to the Fix capitalization feature.)
Regards,
Barry